Keratins are the most abundant proteins in epithelial cells, in which they occur as a cytoplasmic network of 10-12 nm wide intermediate filaments (IFs). They are encoded by an evolutionarily conserved multigene family, with 54 individual members subdivided into two major types (I and II). The pairwise regulation of type I and II keratin genes reflects a strict heteropolymerization requirement. In addition, keratin genes are regulated in an epithelial tissue-type and differentiation-specific fashion. A major role fulfilled by keratin IFs is to act as a resilient scaffold that endows epithelial cells with the ability to sustain mechanical and non- mechanical stresses. Accordingly, inherited mutations affecting the coding sequence of keratins account for several epithelial fragility disorders. Many additional functions, which are non-mechanical in nature and manifested in a keratin- and context-dependent fashion, have been revealed in recent years. In this project we seek to further our understanding of the range, and nature, of non-mechanical functions performed by keratin proteins in skin epithelia, and define the underlying mechanisms. Our central dogma is that such functions are highly relevant to the pathogenesis of chronic diseases such as psoriasis and carcinoma. To that end we will build on our recent discovery, in efforts funded by this grant and focused so far on conventional keratin 17 (K17) and K6 null mice, of novel regulatory roles towards i) translation and cell growth, and ii) Src kinase activity, both events being central to skin epithelial homeostasis. In Aim 1, we will build new mouse models that will further our understanding of the role of keratins during hair follicle cycling, wound repair, and disease. These are keratin 16 (K16) null mice and K16/K17 double null mice, with the K17 null allele targeted so as to allow its conditional manipulation. In Aim 2, we will focus on the functional link between K17 protein and translation, by examining the significance of site-specific phosphorylation of K17 in vivo and searching for additional epithelial contexts (including cancer) in which keratin could impact translation and cell growth. Finally, in Aim 3, we will further assess the significance of the role of K6/K16 during cell migration, primarily by mapping the binding determinants responsible for the keratin-Src interaction and use this information to abrogate it in vivo and assess the associated impact on wound repair and other contexts involving keratinocyte migration. Collectively these studies are predicted to significantly broaden our understanding of the role of keratin proteins in skin epithelial homeostasis in health and disease, and as such may lead to novel therapeutic approaches. PUBLIC HEALTH RELEVANCE: Keratins are the major intermediate filament-forming proteins occurring in epithelia. Recent progress uncovered a new type of function for these cytoskeletal proteins, whereby they bind and regulate cellular proteins involved in signaling and other metabolic pathways. The extent and nature of this non-mechanical role in skin epithelia, its spatial and temporal regulation, and relevance to disease such as psoriasis and cancer, are grossly underestimated at present, and represent the primary focus of the studies performed in this project.